This invention relates to a gas flow measuring device which is useful for measuring the flow of intake air of the engine.
It has heretofore been proposed that a flow measuring pipe is provided in the suction pipe of the engine, an electric heater is provided within this flow rate measuring pipe and temperature dependent resistors are positioned at the front and at the rear of the electric heater to form an intake air flow measuring device. According to this device, accurate measuring of flow is possible in a compact and simple structure. Further, measuring accuracy does not change with the installation status of the device.
However, the device of this type has required such elements as a chopper amplifier, a resistor of high accuracy and a capacitor in order to realize high accuracy despite the changes in temperature characteristics and changes in time of use of the differential amplifier. Such a conventional device amplifies the diametrical voltage of the bridge consisting of two temperature dependent resistors and two reference resistors by a differential amplifier and controls the voltage to be applied to the electric heater so that the voltage output thereof becomes constant.